Abstract: A method and apparatus is provided for characterizing a differential circuit. A measurement system (200) is used to introduce input signals to the differential circuit and to measure corresponding output signals. Particularly, an input differential wave is introduced into the differential circuit (1010) while correspondingly measuring a differential output wave (1020) and a first common mode output wave (1030). Similarly, an input common mode wave is introduced (1040) while measuring a second differential output wave (1050) and a second common mode output wave (1060).

Abstract: A relay circuit comprise first and second relays having respective terminals at which positive cross-talk of a signal of positive polarity is produced when the other terminals to which the positive polarity signal is applied are in the make and break states, respectively, and third and fourth relays having respective terminals at which negative cross-talk of a signal of negative polarity is produced when the other terminals to which the negative polarity signal is applied are in the make and break states, respectively, wherein with regards to the terminals where the cross-talk occurs, the first and fourth relays are connected to each other and said second and third relays are connected to each other, respectively.

Abstract: An overlay selective harmonic transducer device is installed on affected track circuits, that is, track circuits on which interference with normal functioning has occurred due to traction power harmonics.

Abstract: An induction cancellation circuit is used to minimize the effects of AC induced signals appearing on a pair of telephone lines on the activation of a current sensor by a DC loop current flowing on the telephone lines. An input of the current sensor is coupled to one of the telephone lines by a coupling resistor so as to receive energizing potentials from both the AC induced signals and the DC loop current. On the other hand, the having an cancellation circuit includes an amplifier having an amplifier input coupled to the other telephone line by a DC blocking capacitor. The amplifier is biased at unity gain and provides an output signal equal to but 180.degree. out of phase with the AC induced signals received at its input.